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Chapter 10 Post-Acquisition Processing Mask Operations 153
Multiply each pair of corresponding numbers, and sum the products.
(-1 20) + (-1 20) + (-1 19) + (-1 20) +
(8 21) + (-1 20) + (-1 20) + (-1 19) + (-1 20) = 10
The result is placed at position 100, 100 in the output image file. The mask is now placed
over the 9 pixels centered at 101, 100, and the procedure is repeated.
Laplacian masks
The three Laplacian masks on the Edge Enhancement window operate just as described
above. Since the sum of the mask coefficients of the Laplacians sum to zero, the result of
a Laplacian operation on a region of uniform density is zero. Boundary features are
enhanced by varying degrees.
Sobel edge detection
The Sobel edge detection method is more involved, but produces greatly enhanced
features. Number the squares of the subregion of the image as follows:
A
0
A
1
A
2
A
7
A
3
A
6
A
5
A
4
The replacement for the center cell, called R, is
1
R = [X
2
+ Y
2
]
½
where
1
Pratt, William K., Digital Image Processing, John Wiley & Sons, New York, 1978, pp. 487-488.
Figure 130.
Edge
Enhancement
Parameters tab
page.